Measuring method and apparatus

ABSTRACT

A method and apparatus for measuring the dimensions and determining the three-dimensional, spatial volume of objects. In the preferred embodiment, a light curtain and ultrasonic sensing are employed in combination with the travel time of linearly moving objects to ascertain object dimensions. The preferred embodiment is particularly suitable for measurement of moving, rectangular objects of random orientation with respect to the direction of travel.

This is a continuation-in-part of U.S. patent application Ser. No.07/671,256 filed Mar. 18, 1991, now U.S. Pat. No. 5,105,392 which is acontinuation-in-part of U.S. patent application Ser. No. 07/402,213filed Sep. 1, 1989, now U.S. Pat. No. 5,042,015, issued Aug. 20, 1991.

BACKGROUND OF THE INVENTION

The present invention relates generally to the utilization of ultrasonicsound waves and a light curtain in combination to take dimensionalmeasurements of objects and, more specifically, to a method andapparatus for ascertaining three-dimensional measurements and/or volumeof objects.

Millions of packages per year are handled and shipped by United ParcelService, Federal Express, and many other smaller courier and deliveryservices. These packages originate with federal, state, and localgovernments as well as private businesses of all sizes. In manyinstances, the charges by the carriers to their customers are based onthe so-called "dim-weight factor" or "dimensional weight factor" (DWF)of the article being shipped, a fictitious dimension based on lengthtimes width times height in inches divided by a standard agency orassociation-recognized divisor or conversion factor, commonly 166(L×W×H÷166). The "166" divisor or conversion factor has been recognizedand adopted by the International Air Transport Association (I.A.T.A).Even if an object or package is of irregular configuration, the dimweight, using the longest measurement each of length, width, and height,is still utilized for billing purposes. The volume computed bymultiplication of object length times width times height may hereinafterbe termed the "cubic volume," "spatial volume," or simply the "cube" ofthe object.

The measurements of the articles shipped is also critical so that thecarrier can accurately determine the number of trucks, trailers, orother vehicles which will be required to transport goods to theirdestinations and so both customers and carriers can accurately estimatetheir warehousing and other storage needs.

In addition, article weight and measurements are also used to determineand predict weight and balance for transport vehicles and aircraft andto dictate the loading sequence for objects by weight and dimensions formaximum safety and efficiency.

Further, if orders of any items are to be packed into boxes, knowledgeof object weight and dimensions would be useful for selecting box sizeand durability.

To date, it has been a common practice for the customer to manually"cube" or measure boxes or other articles with a ruler, yardstick, orother straightedge marked with units of length, generally inches,perform a calculation for "dim weight," and provide same to the carrierwith the package. If the customer does not "cube" the articles, then thecarrier performs the operation. Since these measurements andcalculations are generally done hurriedly, there is an equal chance thatthe customer will be under or over charged. To add to the problem, thereare many packages and other objects not susceptible to even a grosslyaccurate manual measurement of dim weight, for example and not by way oflimitation, loaded pallets, tubes, drums, reels of hose, cable or wire,etc. Many machine and automotive parts are shipped "naked" with tagsattached or, at most, bagged or shrink wrapped. It is obvious to oneskilled in the art that a straightedge measurement to ascertain thegreatest extent of each dimension will not be accurate in any of theseinstances to any degree whatsoever.

It is known to the inventor that a "jig"-type measuring system forpackages has been used, with a base and two sides joining in a corner at90° angles, each marked with gross dimensional units (to the nearest oneinch) so that a cubic package can be placed on the base at the cornerand measurements taken manually by looking at the markings and recordingsame, but again, the accuracy is limited by the care and eyesight of themeasurer, and the time utilized is unreasonably long when thousands ofpackages are being shipped, as with Sears, K-Mart, or other largeretailers.

In short, a quick, accurate means and method for determining thedimensions and the cubic volume or spatial volume of packages and otherobjects in a commercial or industrial setting has been lacking for manysituations.

U.S. Pat. No. 5,042,015, assigned to the assignee of the presentapplication, discloses a practical and commercially successful means andmethod for object measuring. However, the patented method and apparatusrequires, for measurement of moving objects, that the objects be alignedwith respect to the path of movement. Thus, there existed a need for asystem for measurement of skewed objects. To the best of the inventors'knowledge, only one such commercially offered system exists, and isdescribed in U.S. Pat. No. 4,773,029. The system of the '029 patent,however, senses the apparent dimension of the moving object solelythrough the use of infrared emitter-receiver arrays, and establishes thetrue length and width of an object by periodic measurements whichprovide "slices" of the object, the slices then being summed to providea horizontally planar footprint of the object from which the true lengthand width are measured. The inventors have no knowledge as to whetherthe system in fact works as described in the patent, but its advertisedcost makes it prohibitively expensive, beyond the capabilities of manybusinesses, and a financial burden on those companies able to afford it.

U.S. patent application Ser. No. 07/671,256, filed on Mar. 18, 1991 andassigned to the assignee of the present invention, provides analternative to the system of the '029 patent. The application disclosesand claims a method and apparatus for determining the actual length andwidth dimensions of a linearly moving rectangular object by determiningapparent length, apparent width, and the distance between an objectcorner facing to the side of the travel direction and the trailing edgeof the object. These measurements were then employed to determine theactual object length and width via trigonometrically-based mathematicalequations. The methodology as described in the '256 application has beenproven to be sound, as have the mathematical relationships, but theapparatus described in the application employed to obtain the dimensionshas been found lacking as to the accuracy desired by the inventors.

SUMMARY OF THE INVENTION

The present invention comprises a method and apparatus for rapidly andaccurately determining the length, width and height of packages andother substantially rectangular objects by utilization of a combinationof a light curtain and an ultrasonic distance sensor.

A preferred embodiment of the invention, for determining the length,width and height of a rectangular object skewed in relationship to aconstant speed linear path of travel, such as is dictated by a conveyor,utilizes a light curtain disposed transversely to the path of objectmovement, and one or more downwardly-facing ultrasonic distance sensorsdisposed above the path. Either a separate trigger, such as a photocell,or object intrusion into the light curtain may be used to activate themeasuring sequence of the apparatus. Upon activation, the apparentlength of the object is measured as a function of the travel time of theobject past a given point, such as the photocell or the light curtain.Apparent width of the object is determined by the maximum lateralintrusion by the object through the light curtain to the right and tothe left of the travel path. One other dimension, the distance betweenthe passage of a laterally outwardly protruding object corner and thetrailing edge (corner) of the object, as measured in the direction ofobject travel, is determined by measuring the time between passage ofthe former and that of the latter through the light curtain. From thesethree dimensions, the actual length and width of the object can becomputed.

Maximum length of the object is determined by measuring the travel timesof ultrasonic waves from the downwardly-facing sensor reflected from theobject during the object's passage thereunder as the sensor is firedmultiple times, taking the shortest travel time, converting it to adistance, and subtracting it from the known distance between the sensorface and the conveyor surface. To measure objects on wide conveyorsurfaces a bank or array of sensors may be deployed to cover the entirelateral extent of the conveyor.

The width, length and maximum height of the object may then bemultiplied to compute the cubic volume or spatial volume of the objectfor billing, storage, packing or other desired purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood by one skilled inthe art through a review of the following detailed description of thepreferred embodiments taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 comprises a schematic top elevation of a first preferredembodiment of the present invention;

FIG. 2 comprises a schematic side elevation of the embodiment of FIG. 1;

FIG. 3 comprises a perspective elevation of a second preferredembodiment of the present invention;

FIG. 4 comprises a top elevation of the embodiment of FIG. 3 with thejig removed from the support housing;

FIG. 5 comprises a macro schematic for the electronics associated withthe present invention;

FIG. 6 comprises a block diagram of the control unit associated with thepresent invention;

FIG. 7 comprises a flow chart of the operating sequence of the presentinvention.

FIG. 8 comprises a perspective view of a preferred embodiment of ameasuring station for large loads in accordance with the presentinvention;

FIG. 9 comprises a schematic top elevation of one embodiment of theinvention for determining the length and width of an object skewed withrespect to the path of a conveyor on which it is moving;

FIG. 10 comprises a schematic top elevation of a preferred embodiment ofthe invention utilizing a photocellbased detector and control system fora conveyor-fed weighing and measuring station;

FIG. 11 comprises a flow chart of an improved method for calibratingultrasonic sensors.

FIG. 12 comprises a schematic top elevation of a preferred embodiment ofthe invention for determining the length and width of an object skewedwith respect to the path of a conveyor on which it is moving; and

FIG. 13 comprises a perspective view of the apparatus of FIG. 12,showing in addition the deployment of a bank of ultrasonic heightsensors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Ultrasound technology is extremely safe, emitting no radiation; visible,ultraviolet, or infrared light; audible sound; odor; or heat. Further,ultrasound, as used in the present invention, will not damage a packageor its contents during the measurement operation. Finally, theultrasonic sensors utilized in the present invention has no moving partsand is essentially maintenance free.

The preferred ultrasonic transducers or sensors employed with thepresent invention are electrostatic, although piezoelectric transducersmay be employed. The preferred electrostatic sensors operate at afrequency of 49.6 kHz with a maximum current draw of 130 milliamps at12-17 volts DC. Suitable sensors are potted electrostatic transducers instainless steel housings with circuit cards produced by LundahlInstruments, 710 North 600 West, Logan, Utah 84321, while the transducerunits themselves are manufactured by Polaroid and Texas Instruments. Thesensors are operable over a temperature range of 0 to 50 degrees C. andat relative humidity levels of 90 percent or less, noncondensing. Thehigher frequency (>120 kHz) piezoelectric sensors are not preferred dueto the fact that, while their resolution exceeds that of theelectrostatic transducers, they are also highly directional so as torequire multiple transducers to sweep a particular dimension if widelyvarying sizes of packages and package profiles are to be encountered. Inaddition, the directionality requires a precise orthogonality of theside of the object to be measured relative to the sensor.

Referring now to FIGS. 1 and 2 of the drawings, top and side views,respectively, of a first preferred embodiment of the invention aredepicted in schematic form. Dynamic measurement unit 10 of the presentinvention comprises three ultrasonic transducers or sensors 12, 14, and16, deployed at conveyor means 18, conveyor means 18 being a belt-type,roller-type, tow line or other conveyor, as known in the art. Anautomated guided vehicle (AGV) may also be employed to carry or move theobject past the sensors. Sensors 12, 14, and 16 are functionallyidentical and interchangeable.

As shown by arrow 20 in FIG. 1, the direction of motion in this exampleis left to right. Given that orientation of movement, photocell 22 andretroreflector 24 are preferably mounted substantially in lateralalignment with sensors 14 and 16 so as to trigger a measurement when theleading edge of a large object 28 or small object 26 interrupts thelight beam between photocell 22 and reflector 24. Photocell 22 may beany commercially available photocell, preferably operating in theinfrared polarized light range. Proximity sensors of various types,including but not limited to magnetic or capacitive, may also beemployed. A suitable photocell polarized with a sunlight immunity of10,000 foot candles is the Model 1456A-6517, manufactured by Opcon of720 80th Street, S.W., Everett, Wash. 98203-6299. Polarization isdesirable to eliminate problems with reflectivity of the object breakingthe photocell beam.

Sensor 12, as shown, is utilized to measure the length of object 26 or28, "length" being an arbitrary term used in this instance to designatethe dimension of an object taken in a direction parallel to that of thedirection of conveyor motion 20. Sensor 12, as shown in FIG. 1, ismounted horizontally and substantially parallel but at a slight angle αto the direction of motion of the conveyor means 18. Sensor 12 ismounted so that is to the side 30 of conveyor means 18 with whichobjects 26, 28 have been previously aligned. Such alignment may beaccomplished by any means known in the art such as a set of angled orskew conveyor rollers upstream of station 10. The reason for thisalignment will be explained hereafter in detail. The slight angularorientation and lateral offset of sensor 12 from conveyor means 18 iseasily compensated for by simple geometrical calculations, it beingappreciated that to place sensor 12 in alignment with the conveyor meansmotion would result in it being hit by objects thereon or requiring somemeans to raise and lower the sensor or swing it into a position afterthe object has passed.

Sensor 14, as shown, is utilized to measure the width of object 26 or28, "width" being an arbitrary term used in this instance to designatethe dimension of an object taken in a direction horizontallyperpendicular to the direction of conveyor motion 20. Sensor 14 is alsomounted in a horizontal attitude and to the side 32 of the conveyormeans 18 opposite t he side 30 thereof where object alignment has takenplace. Sensor 14 should be mounted, as shown in FIG. 2, just high enoughabove the surface 34 of conveyor means 18 so that its ultrasonic waveswill not be reflected by surface 34 but not so high that the waves,which spread in a generally conical pattern from the sensors with anincluded angle β of 7 to 12 degrees (shown greatly exaggerated in FIG.2), will miss the lowest object, such as small flat object 26, the widthof which is to be measured by station 10.

Sensor 16, as shown, is utilized to measure the height of object 26 or28, "height" being an arbitrary term used in this instance to designatethe dimension vertically perpendicular to the direction of conveyormotion 20. Sensor 16 is mounted in a vertical attitude and preferablyadjacent to and to the inside of the side 30 of conveyor means 18whereat alignment takes place. Of course, it should be placed above thesurface 34 of conveyor means 18 at a height great enough so as to clearthe tallest object placed on surface 34.

Once the sensors 12-16 have been mounted, a "zero point" for objectmeasurement is established. This "zero point" 36 coincides with anobject having zero length, zero width, and zero height and can beanywhere on the length of conveyor means 18 but must be, for thisembodiment, on the side 30 where objects 26 or 28 are aligned.

After sensors 12-16 are mounted and the zero point 36 selected, thepositions of sensors 12-16 are adjusted in response to placing a targetobject of known dimension in the measuring field or volume adjacent zeropoint 36, as shown in FIGS. 1 and 2, and triggering the sensors thensubsequently adjusting the sensor positions and resulting system outputuntil it corresponds to the known values. A one foot cube, twelve incheson a side, is typically utilized as reference. The dimensions of theobject measured by sensors 12-16 are directly related to travel time ofthe ultrasonic waves emitted and reflected. For length sensor 12, theinterruption of the infrared beam between photocell 22 andretroreflector 24 by the leading edge of the object to be measuredtriggers initial measurement of the distance X₁ between the face ofsensor 12 and the trailing edge of the object to measured.

Distance X₁ is then geometrically corrected for angle α to a truedistance between sensor 12 and the trailing edge of the object andsubtracted from known distance X₂ between sensor 12 and zero point 36 togive the length dimension X of the object (X=X₂ -X₁).

To measure the width of an object, sensor 14 is triggered by photocell22 and measures the distance Y₁ between the face of sensor 14 and thenear side edge of the object. Since the distance Y₂ between sensor 14and the zero point 36 at side 30 of conveyor means 18 is a knownconstant, the width Y of the object is equal to Y₂ -Y₁. In similarfashion, the height distance Z₁ is measured between the face of sensor16 and the top of the object and subtracted from the known distance Z₂between sensor 16 and surface 34 to provide the height Z of the measuredobject.

It should be understood that the term "measure" does not necessarilyindicate that only a single measurement is taken of each dimension byeach sensor. In fact, measurements can be taken numerous times in aburst of ultrasonic waves which re emitted, reflected, and received.However, such multiple measurements are not deemed necessary and aretherefore not preferred due to the additional time required. Forexample, measurements may be taken sequentially for 0.17 second by eachsensor at a rate of 12 times per second and the resulting wave traveltime signals for each sensor averaged to give a value X₁, Y₁, or Z₁. Itis thus apparent that such an approach would take over 0.5 seconds forthree-dimensional measurement, a major consideration and a disadvantagewhen the object measured is moving at a high rate of speed. Utilizingthe sensors previously referred to above, dimensional measurements canbe taken with dynamic measurement unit 10 to an accuracy of ±0.1 inches.

Due to the fact that measurements are taken while the conveyor means 18is carrying objects past dynamic measuring unit 10, it is necessary tocompensate the length measurement for the speed of the conveyor means insome manner. An adjustment in data calculations by a microprocessor usedto control unit 10 is one solution. The speed of conveyor means 18 isknown a priori. The "lag time" between triggering and firing of thelength sensor 12 is a constant which is calculated or measured. If thelag time is multiplied by the conveyor means speed, this produces the"lag distance," i.e., the distance an object will travel on conveyormeans 18 between triggering and firing of sensor 12. The lag distancecan then be added via the software in a processor to the sensed(incorrect) distance to yield true length.

A simpler and more preferred solution for conveyor speed compensation isto move photocell 22 and retroreflector 24 along conveyor means 18upstream of zero point 36. If an object of known length is placed onconveyor means 18, a measurement triggered by photocell 22 is taken andthe measured length is too short, photocell 22 is moved upstream fromzero point 36. For a conveyor means carrying objects at 90 feet perminute past unit 10, the final photocell position will normally be 0.7inches upstream of zero point 36.

In lieu of moving photocell 22, the position of length transducer orsensor 12 may be altered. If the article length is measured as ittravels away from sensor 12 on conveyor means 18, sensor 12 can be moveddownstream by the lag distance units of length. If article length ismeasured as it travels toward sensor 12, sensor 12 is also moveddownstream by the lag distance.

Optionally, in lieu of utilizing ultrasonic sensor 12 for lengthmeasurement, length may be measured using the photocell 22, thetriggering thereof by an object commencing a clock timing which, whencorrelated to the speed of the conveyor means, results in an accuratemeasurement of length directly related to the time between whichphotocell 22 is switched off by an object and the time it is turned onagain when the trailing edge of the object passes. The known speed ofthe object (conveyor speed) is multiplied by the "dark time" duringwhich the light beam of photocell is interrupted and the object lengththereby ascertained. This technique may also be employed with thepreviously referenced proximity sensors.

While unit 10 has been described in terms of a single embodiment, otheroptional configurations are available and achievable. For example,instead of aligning objects with side 30 of conveyor means 18, they maybe placed randomly anywhere on conveyor surface 34 so long as they arestraight or aligned with the direction of motion. In such an instance,two sensors, 14a and 14b, are placed directly opposite one anotheracross conveyor means surface 34, and both are triggered at the sametime, sensor 14a measuring a distance Y₁, 14b measuring distance Y₂, andY₁ and Y₂ being subtracted from known distance Y₃ between the faces ofsensors 14a and 14b to give width Y of the object.

Length sensor 12 may also be placed aiming upstream with respect tomotion 20 and placement adjusted accordingly with respect to zero point36. If software compensation is employed, the lag distance is thensubtracted from the measured distance to arrive at the correct length.

If extremely wide or tall objects of uneven configuration are to bemeasured, such as pallets loaded with boxes or other merchandise,several sensors 14 and 16 may be placed at adjacent locations to coverthe entire possible width or height to be encountered.

Finally, it may be desirable to simultaneously weigh the objects beingmeasured at unit 10. For this purpose, weighing unit 40 may be placedunder surface 34 of conveyor means 18 and triggered by photocell 22 inthe same manner as sensors 14-16 by photocell 22. One suitable devicefor on-the-fly weighing is the Weigh-Tronix Model CVSN-3660-200,manufactured by Weigh-Tronix, Inc. of 1000 Armstrong Drive, Fairmont,Minn. 56031. Of course, the weighing device 40 utilized depends upon thedesign loads of unit 10.

If an AGV is utilized to move objects past sensors 12-16 of a unit 110,the weighing unit 40 may be placed under the floor and the scale taredto the weight of the unloaded AGV.

It should be noted that ultrasonic waves generated by sensors 12, 14,and 16 of the type employed in the present invention are affected intheir travel time by temperature, barometric pressure and humidity andthat it is therefore desirable to compensate for variations in same whenprocessing the measured travel times. Such compensation can be vialook-up tables in a computer memory or by microprocessor correctionusing known equations for the effects of these variables. However, thepreferred method of the present invention is to use the wave travel timefor a known distance to compensate for these effects.

For example, in dynamic unit 10 and in subsequently described staticmeasurement unit 110, the height measurement sensor 16 is triggered whenno object is present in the measuring field or volume. The height sensoris utilized because of the large target presented by the conveyorsurface (unit 10) or platen (unit 110), as the case may be. Since thedistance between the face of sensor 16 and the target is known, thenumber of "counts" of the high frequency clock in the control system 202associated with the present invention per inch of measured distance canbe computed. For example, if the nominal time per unit distance roundtrip in "counts per inch" is 590, using a clock frequency of 4 MHz and ameasurement by sensor 16 of a known 30 inch distance therefore normallyproduces 17,700 "counts" of travel time, in the event that the traveltime takes 17,730 "counts," the system self-adjusts to utilize 591"counts per inch" as the time per unit distance reference to accommodateto longer wave travel time. This corrected figure is then applied to theactual object measurements made using sensors 12-16 in order to producea more accurate result.

The calibration of the system is self-commanded upon startup (see FIG.7) and is periodically repeated in response to software commands or,optionally, may be induced periodically by a timer circuit command.

It is also desirable to provide an override for measurements in excessof the maximum design dimension to be measured falling in the "nearfield space" in front of the sensors, as the travel time of thereflected ultrasonic waves is too short for accurate processing givenreaction time lags in the sensors and processing equipment. Therefore,it is desirable to provide so-called "blanking zones" for a certaindistance in front of the sensors where no measurements will be taken forwave travel times below a certain minimum. Finally, it is desirable toadjust the sensitivity of the sensors to respond as receivers only to aminimum amplitude of reflected signal or echo from the objects beingmeasured in order to avoid spurious measurements attributable to otherobjects or structures within range of the sensor.

Referring now to FIGS. 3 and 4 of the drawings, stationary measuringunit 110 will be described in detail. Unit 110 includes the same basiccomponents as unit 10 but in a substantially different configuration. Asin unit 10, sensors 12, 14, and 16 measure the length, width, and heightof a small object 26 or large object 28 and are preferably identical tothose of unit 10. In this instance, however, the sensors are mounted ona jig 112. Due to the measured object being stationary whilemeasurements are taken, the accuracy of unit 110 is greater than that ofdynamic unit 10 and may approach ±0.01 inches.

Jig 112 comprises three arms 114, 116, and 118 disposed at mutuallyperpendicular angles to one another so as to join at corner 120 whichalso serves as the "zero point" for unit 110. Jig 112 is fabricated fromheavy gauge sheet stock, such as anodized aluminum, and comprises base122, left side 124 and right side 126. Base 122 includes object supportplaten 128 and arm extensions 130 and 132. Left side 124 includes armextensions 134 and 136 which meet at crotch 138. Right side 126 includesarm extensions 140 and 142 which meet at crotch 144. Arm extensions 132and 142 join at a 90° angle and coextensively form arm 114, armextensions 130 and 134 join at a 90° angle and coextensively form arm116, and arm extensions 136 and 140 join at a 90° angle andcoextensively form arm 118. At the end of each arm, sensor mountingplates 146, 148, and 150 hold sensor 12, 14, and 16, respectively, inpositions parallel to their respective arms 114, 116, and 118 and aimedinwardly at zero point 120.

Jig 112 is mounted on support housing 156 via load cell 154 which shownin broken lines under base 122. Support housing 156, like jig 112, isfabricated of heavy gauge sheet stock. Load cell 154 is preferably ahigh precision steel-type load cell, and a suitable model using a dualbridge strain gage is Model No. 60048A, available from Sensortronics of677 Arrow Grand Circle, Covina, Calif. 91722. Load cell 154 is rigidlyanchored at its bottom to the bottom of support housing 156, as bybolts, and its offset top to base 122, again as by bolts. Load cell 154is designated to accept off-center loads and so is ideally suited forits application in unit 110 where, as shown in FIG. 3, object 28 has alength greater than its width. However, it was unexpectedly discoveredthat load cell 154 could be utilized as the single weighing means withunit 110 even if the load is significantly off-center without anoticeable diminution of accuracy so long as the horizontal axis of theload cell is oriented toward the zero point 120 of unit 110 and on aline of symmetry at the midpoint (45°) of the 90° angle between arms 114and 116. The distance of load cell 154 from the zero point 120 isimportant as is the direction load cell 154 is facing (either toward oraway from zero point 120) due to the differing amounts of torque exertedon load cell 154 by platen 128 and the object being measured. However,the foregoing is not as critical as the alignment symmetry of the loadcell.

Support housing 156 is equipped with four small screw-type jack stands158 to accommodate loads in excess of the rated capacity of load cell154 so as to prevent damage thereto. Support housing also accommodatesintegral electronics 160 for unit 110 which will be described furtherhereafter. Internal electronics 160 comprises a rack-mounted assemblyslidably disposed behind cover plate 160 of support housing 156, theassembly communicating with sensors 12, 14, and 16 via cables 162 andconnectors 164 as is well known in the art, connectors 164 mating withother connectors and cables (not shown) running outside support housing156 to the sensors to a power supply and to external electronics whichmay include a bar code reader, triggering switches, a host computer,and/or a display means such as a printer or LED display, etc.

After the dimensions of an object are measured, the volume thereof maybe computed, the dimensions added to determine girth of the object ormay be sorted to classify objects as to one or more dimensions. As notedpreviously, weight may also be ascertained with unit 10 or unit 110.

The dimensional data may, of course, be displayed via LED or otherdisplays as known in the art and calculated by hand. However, it ispreferable that the measuring and calculating operations be controlledand performed by a programmed processor. It will be understood by thoseskilled in the art that English or metric units may be employed indisplays or other outputs as well as in calculations.

One potential control and processing system for sensors 12, 14, and 16is schematically depicted in FIG. 5. The system as depicted includes asingle transducer or sensor designated by way of example as 12 which isultimately controlled by a process controller 180. Unit 180 does, infact, control sensors 12, 14, and 16, but for simplicity's sake, only asingle sensor is shown. Sensor 12 is triggered by the interruption by anobject of the beam 23 between photocell 22 and retroreflector 24 (FIG.5) in the instance of unit 10 and by the operator in the case of unit110. Process controller 180, in response to photocell 22, produces atrigger signal sent to pulser 202 and counter/timer 204 causing pulser202 to transmit an activation signal to sensor 12 and counter/timer 204to start counting. If static measurement unit 110 is being controlled,pulser activation may be triggered by a timer, footswitch, softwarecommand, or other suitable means via unit 180. The pulser signal causessensor 12 to transmit an ultrasonic signal burst toward the object to bemeasured. Generally, each burst of ultrasonic signals comprises one tofour signals. It is desirable, as noted previously, to provide avariable amplitude control which may be provided in pulser 202 orcontrolled by unit 180 but is preferably included in sensor 12. Pulser202 signals sensor 12 via electrical cable (not shown in FIGS. 1-4) in amanner well known in the art. The ultrasonic signals are reflected fromthe object to be dimensionally measured and received by sensor 12whereupon they are converted to electrical signals. Sensor 12 containssignal detection circuitry to convert the electrical signals to signalssuitable for manipulation by process controller 180. Such circuitry isknown in the art and includes means for adjusting sensitivity such asvariable threshold circuit, a variable amplifier for increasing theamplitude of signals relayed to the processor from the sensor, and/or(as noted above) circuitry for boosting the amplitude of the pulsersignals sent to the sensor.

Signals received by sensor 12 from the object reflecting the ultrasoundwaves are amplified by an amplifier therein and wave shaped by acomparator associated therewith, with the latter being synchronized withthe incoming signals from pulser 202 so that the comparator output isalways positive. The gain of the amplifier and the threshold of thecomparator are preferably controllable at sensor 12.

As noted above, timer 204 is controlled by a start input from processcontroller 180 and a stop input from sensor 12. When pulser 202 istriggered by unit 180, counter/timer 204 is started, and when an outputsignal is received from sensor 12, counter/timer 204 is stopped. Thus,the time interval between a transmitted sensor pulse and the receipt ofa reflected sensor signal is measured and output to process controller180 wherein the time interval is converted first to a distance and thento a dimension of the measured object. Of course, system delays (i.e.,time lags due to circuitry and components) must be compensated for, asknown in the art, unless the outgoing signal time lags and incomingsignal time lags cancel.

Process controller 180 communicates with input/output means 206 whichcan comprise a host computer such as any commercially available personalcomputer or a dumb terminal in more sophisticated operations, a largercomputer controlling numerous measuring stations. The output of the unit180 can be digitally displayed, as on a computer screen or via LEDdisplay, can be produced as hardcopy via printer or can be relayed tomemory (RAM, hard disc, floppy disc) associated with an input/outputmeans 206 and/or transmitted to any other location desired.

In order to correlate a measurement series (length, width, height) andcalculated volume or total dimensions with a particular object measured,bar code reader (BCR) 208 is utilized to read a bar coded sticker orlabel affixed to the object measured, either before or after themeasurement has taken place. Bar code reader 208 preferably outputs toprocess controller 180 but may alternatively output to input/outputmeans 206.

As noted previously, both units 10 and 110 may optionally incorporate aweighing means or scale 210 to weigh the object measured simultaneouslywith the dimensional measurement. Preferably, weighing means 210 istriggered by process controller 180 and outputs thereto, and thendimensions, volume and weight output from process controller 180 toinput/output means 206. Weighing means 210 may alternatively provideweight data directly to input/output means 206 in a form readable bymeans 206 for display, memory, or further transmission.

While process controller 180 has been referred to merely as a singlecomponent, it will be understood by those skilled in the art that theterm "process controller" may, and in fact does, encompass a pluralityof components, including a microprocessor, memory, data bus, addressbus, timing and control bus, registers, and an interface device such asan input/output controller. The process controller may be custom-builtfor use with unit 10 or 110 or may be a commercially available unitprogrammed to act in the manner desired. In any event, the hardwareinvolved is well known to those skilled in the art. FIG. 6 depicts apreferred embodiment of a control unit 200 in the form of a blockdiagram wherein all of the component elements of process controller 180,pulser 202, and counter/timer 204 are all incorporated as a partthereof.

Referring to FIG. 6, the preferred embodiment of the control unit 200associated with the present invention includes a number of componentsknown in the microprocessor/computer art, the major ones of which willbe discussed below. Briefly, control unit 200 includes a centralprocessing unit (CPU) 212, address bus 216, data bus 214, a controlcircuit 218 which commands memory 222, data input/output 224, pulser202, and counter/timer 204 via timing and control lines 220 (which mayalso be referred to as a timing and control bus 220).

Control unit 200 communicates with an input/output means 206, aspreviously noted, via bus or cable 230, while pulser 202 communicateswith sensors 12, 14, and 16 via bus or cables 226. It should be notedthat sensor output signal line 234 extends from bus 226 to provide a"stop" signal to the counter/timer 204 as previously described withrespect to FIG. 5.

CPU 212 preferably comprises an 8 bit Zilog Z84C00 microprocessor.Address bus 216 and data bus 214 are entirely conventional and will notbe described in detail. Control circuit 218 includes one or more addressdecoders and a plurality of logic gates (latches) to control, via lines220, the type and sequence of operations performed by the system asdetermined by CPU 212. Memory 222 preferably comprises two 8 kbit×8EPROM's, one serving as storage for the mathematical operationsperformed by the system and one as storage for the program master memoryfor CPU 212. In addition, memory 222 preferably includes an 8 kbit×8static RAM for temporary data storage and calibration factors used incorrecting sensor measurements. Data input/output 224 preferablycomprises a Zilog Z84C42 Serial Input/Output Controller and a MAX232Signal Driver, produced by Integrated Maxim Products, 120 San GabrielDrive, Sunnyvale, Calif. 94086, for modifying the system's TTL protocolto RS-232. Pulser 202 comprises a conventional tri-state latch forsequentially triggering sensors 12, 14, and 16. Counter/timer 204includes a plurality of conventional line buffers and drivers and aZilog 284C30 Counter/Timer Circuit including a 4 MHz clock.Counter/timer 204, via the serial input/output controller, determinesthe communication baud rate of the RS-232 interface, in this instance,preferably 9600 baud. The counter/timer circuit can also be employed toinitiate periodic maintenance routines to auto zero the system, or, asin the preferred embodiment, such initiation can be software commanded.

The program language is Z80 assembly, as dictated by the selection ofthe Z84C00 CPU, although the numerical processing portion of the programusing floating point arithmetic is in "C", cross compiled to Z80assembly.

It will be appreciated by those skilled in the art that many alternativecircuit components and other program languages may be employed in andwith the present invention. The foregoing specifically noted elementshave been provided by way of example only and are not to be construed asin any way limiting the present invention thereto.

Preferably, the input/output means 206 communicates with control unit200 via an RS-232 cable, modem, or other suitable interface utilizing anEIA RS-232-C serial communication protocol and employing encoded ASCIIor EBCDIC. Other protocols may be employed such as IBM bisynchronous,3270, SNA, HDLC, SDLC, and others. If control unit 200 is used with ahost computer, control unit 202 recognizes and responds to the followingcommands from input/output means 206:

M -- Measure. This command may be sent by the host computer or may beinitiated directly via a signal from photocell 22, in the case ofdynamic memory unit 10, or from a hand or foot switch in the case ofstatic measuring unit 110.

I -- Install. This command sets up and calibrates the sensors uponinitial installation of the unit.

C -- Calibrate. This command, issued by the host computer 206 orself-commanded by control unit 200 after an object is measured, causescontrol unit 200 to trigger height sensor 16 and to subsequently performinternal humidity and temperature compensation as heretofore described.

R -- Reset. This command, which may be entered manually on control unit200 via a push button or received from host computer 206, clears allregisters and wait conditions in the control unit and causes controlunit 200 to recalibrate itself.

T -- Test. This command causes the measurement process to start andrepeat until any other command is received.

S -- Send Status. Received from host computer 206. Control unit 200normally responds "O" for okay, meaning communications between the twovia RS-232 interface are operable.

B -- Bad transmission. Host computer 206 sends to control unit whentransmission therefrom was garbled or otherwise not understood. Controlunit 200 then retransmits the last data field to host computer 206 frombuffer memory. Conversely, control unit 200 will send a "B" to the hostcomputer 206 if a command is not received properly or not understood.

Control unit 200 will also recognize certain command set outputqualifiers which are set by sending a qualifier letter from the hostcomputer and remain in effect until the same letter is sent again, untilthe system is reset, or at system power up.

D -- Display count. This causes transmission of certain register countsfor diagnostic purposes.

A -- Actual measurement. Will cause control unit 202 to send an actualmeasurement even if less than a preset minimum threshold value.

E -- Error output. Causes control unit 200 to send a signal to hostcomputer 206 if there is a hardware error in sensor 12, 14, or 16.

The foregoing commands are exemplary only and are not to be construed asdefining or otherwise limiting the commands which may be employed withcontrol unit 200 or the present invention as a whole.

FIG. 6 comprises a flow chart of the operation of unit 10 or unit 110.The chart is generally self-explanatory, the exception being the"control or status request" block wherein sensor status may be queried,the display format altered, or the output units (metric, English)changed. It will be noted that the length measurement is triggered firstwhich is desirable in unit 110 due to the movement of the measuredobject. Measuring length first reduces the amount of transducer orphotocell movement or software correction required to compensatetherefor. Height and width measurements may interchangeably be madesubsequent to length, and the scale or other weighing means is triggeredlast to permit, in either unit 10 or 110, the system to stabilize romthe weight and/or impact of the object reaching the scale portion of theconveyor or hitting the platen. The bar code may be read last, as shownin FIG. 7, first or at any other time.

It will be appreciated that the low power draw of the present invention,less than one ampere, renders the system easily adaptable to batterypower, and, in fact, commercially available, non-interruptable powerdevices such as are generally used to power lights and equipment duringpower failures may be employed as power sources for portableinstallation of the present invention.

The previously described embodiments of the invention, while suitablefor parcels and other objects of substantial size, are nonethelesspoorly adapted to weigh and to measure the cubed volume of a stack orpile of articles on a pallet such as would be used in air freightoperations. To that end, the embodiment 300 disclosed in FIG. 8 of thedrawings has been developed.

Measuring station 300 is adapted for use with palletized or other largeloads, including but not limited to, those handled by air freightcarriers, trucking companies, and warehousing operations wherein a forklift or other suitable pallet handling device transports a load 302 ontoweighing deck 304 of a suitable platform deck scale such as the lowprofile Weigh-Tronix Model No. DSL 6060-05, available from Weigh-Tronix,Inc. This particular model of scale has been chosen by way of exampleand not limitation as a standard air freight pallet measures 52" on aside, and the selected Weigh-Tronix scale provides a square platform ordeck 60" on a side, thus easily accommodating load 302 and defining amaximum horizontal target field.

When the load 302 is in position over weighing deck 304, substantiallyparallel to the sides thereof and preferably substantially centeredthereon, it is lowered onto the deck 304 and the weight measured. Atsubstantially the same time, four (4) downward-facing multiplexedultrasonic height sensors 306 on gooseneck arm 308 are simultaneouslyfired. Sensors 306, which are disposed at a common distance above deck304, emit ultrasonic waves having substantially identical velocities atthe same time, and the first returning signal reflected from load 302thus indicates the closest or, in this instance, the highest part of theload. The first returning signal is accepted by a control unitassociated with the sensors, converted to a distance in the mannerpreviously described, and subtracted from the known height of the sensorface above weighing deck 304 to provide the height of load 302. Theremaining three reflected signals are gated out and thus disregarded.While sensors 306 have been depicted in a linear array, otherarrangements such as a square array or diamond array are contemplated,the optimum configuration being dependent upon the size and shape of thehorizontal target field.

A bank of four (4) multiplexed ultrasonic width sensors 310substantially parallel to, above and facing one side of deck 304 isactivated to simultaneously emit ultrasonic waves from each sensor 310and receive those reflected back from the side of the load 302 nearestto them. The first returning reflected signal represents the shortestdistance to load 302 and thus the closest point on the side of the loadagainst which sensors 310 are arrayed. As with height sensors 306, allbut the first returning signal from the bank of sensors 310 arediscarded. Sensors 312, arrayed in a multiplexed bank of four (4)substantially parallel to and above the side of the deck 304, oppositethat adjacent sensors 310, operate in the same manner, being firedsimultaneously at the load 302. The first returning reflected signal isselected as indicative of the point on load 302 closest to sensors 312,and the three remaining signals discarded. The first returning signalsfrom sensors 310 and 312 are converted to distances, the two distancesare added together and then subtracted from the known, previouslymeasured distance between the opposing banks of width sensors 310 and312 to obtain the width of load 302.

The depth of load 302 is determined by a combination of a bank of four(4) laterally spaced ultrasonic sensors 314, parallel to the front sideor edge of deck 304 which is perpendicular to the sides abutted bysensors 310 and 312 and an infrared (IR) light curtain system at therear edge or side of the deck 304, provided by IR emitter 316 and IRreceiver 318, one suitable light curtain system being the BEAM-ARRAYSystem offered by Banner Engineering Corporation of Minneapolis, Minn.In the preferred embodiment, a one-foot length Model No. BME148A emitteris employed in alignment across weighing deck 304 with a one-foot ModelNo. BMR148A receiver. Emitter 316 employs infrared light emitting diodes(LED's) on 0.25 inch centers, and receiver 318 employs phototransistorscentered on the same intervals. The LED's are fired sequentially alongthe length of the emitter 316 at a rate of four milliseconds per foot ofemitter length. Each emitted LED IR beam is directed to itscorrespondingly aligned phototransistor in receiver 318. Emitter 316 andreceiver 318 extend in parallel along opposing sides of the scale deck304 inwardly from rear edge 320 of deck 304. To obtain load depth, thedistance from the front edge 322 of the load 302 to sensors 314 ismeasured ultrasonically, using the first reflected signal acceptancetechnique previously described with respect to the height and widthsensors, and the location of the rear edge 324 of load 302 is determinedby a light curtain from emitter 316, which is broken by the rear edge324 of the load 302. The ultrasonically measured depth distance from thefront edge 322 of load 302 is then added to the detected distancebetween the IR light curtain break and the rear edge 320 of the scaledeck 304 and that sum subtracted from the known distance between thebank of sensors 314 and the rear edge 320 of deck 304 to obtain the loaddepth.

It should be noted that measuring station 300 is easily adapted,depending upon the measurements desired or required by the user, todetermine either pallet dimensions or the dimensions of the load restingon a pallet. Such adaptation is effected by placing ultrasonic sensors310, 312, and 314 and emitter 316 and its companion receiver 318 at theappropriate height above deck 304. If placed just above deck 304, thesensing devices will respond to the pallet dimensions, while if placedsufficiently above the level of the pallet top, the sensing devices willrespond to the objects thereon rather than the pallet itself.

The height, width and depth dimensions of load 304 may then bemultiplied by a control unit associated with embodiment 300 to obtainthe "cube" of the load and the data from measurement and weighing of theload stored in local memory associated with the embodiment 300 alongwith identifying indicia provided by a bar code reader, other automaticcoding source, or manual entry. Alternatively or in addition, the dataand load identifiers may be transmitted in real time to another locationfor storage or further action. As data acquisition, processing andstorage activity has been previously described herein in substantialdetail with respect to other embodiments of the invention, no furtherdetails thereof or the hardware for effecting same in the embodiment ofFIG. 8 are believed to be necessary. However, it should be recognizedthat each sensor bank of embodiment 300, as alluded to above, ispreferably controlled by a multiplexor, each multiplexor being in turncontrolled to sequence the measuring operation by a master multiplexor,which also controls the scale and the IR light curtain emitter/receivercombination in this embodiment. The use of multiplexors being well knownin the art and such devices being commercially available from a varietyof vendors, the control and data acquisition system for the embodimentof FIG. 8 will not be further described.

The use of a plurality of laterally adjacent, similarly orientedultrasound sensors in a bank is viewed as desirable to obtain the mostaccurate distance measurement possible between a side or the top of apalletized or other large load and the sensor bank, given the relativelylarge size of the load. The exact number of sensors employed in a bankis related to the maximum load dimension parallel to the sensor bank,the distance from the sensors to the load, the potential forirregularity of the load surface, and the required accuracy ofmeasurement.

While embodiment 300 of the invention has been described as utilizing anIR light curtain in conjunction with ultrasonic sensors, it should benoted that an allultrasonic system might be employed. For example, abank of sensors could be swung into position on a gate arm behind load302 after its placement on deck 304. Alternatively, the sensor bankcould swing up from the floor where it is protected by a grate or othermeans to support a forklift driving thereover.

The heretofore described embodiments of the invention, while suitablefor measuring objects located anywhere within a given field, stillrequire that the side of square or rectangular objects be aligned in asubstantially perpendicular orientation to the ultrasonic sensor or bankof sensors to obtain accurate measurements of width and length. Such analignment may be effected, as previously noted, by a skew conveyor or byhand. Since objects of square or rectangular shape comprise the vastmajority of those shipped in commerce, alignment becomes a criticalpart, and limitation, of the measuring process. This limitation,however, is overcome in the embodiment 400 of FIG. 9, shown inassociation with a linearly moving conveyor 402. System 400 includes athrough-beam photocell system including an infrared (IR) LED emitter 404and phototransistor receiver 406 mounted directly across the conveyorfrom one another along a line perpendicular to the conveyor path. Athrough-beam photocell system signals when an emitted or outgoing lightbeam is not received, in contrast to a reflector-type system whichsignals when a beam normally reflected from a target does not return tothe emitter/receiver. As a result, even polarized, reflectortypephotocells may give false readings from reflective surfaces of tape andstretch or shrink-wrap films widely employed in packaging. Twoultrasonic sensors 408 and 410 are mounted, respectively, at the samelocations as or immediately adjacent to emitter 404 and receiver 406 andare aimed perpendicularly to the path 412 of conveyor 402.

When an object 420 to be measured passes down conveyor 402, the leadingedge or point 422 thereof breaks the photocell beam, resulting in thecommencement of a timed "dark" period until the beam is again unbrokenby object 420, the speed of the conveyor 402 being a known constant andpermitting the user of the system to easily determine distance "Y"parallel to the conveyor path in a manner as previously describedherein. The obstruction of the photocell beam also initiates therepeated triggering of the ultrasonic sensors 408 and 410, the readingsfrom which ramp or vary as the ultrasonic signals repeatedly reflectfrom the obliquely oriented sides of the object 420 as its corners 424and 426 first approach and then pass sensors 408 and 410, respectively.As a result, distance "X" perpendicular to the conveyor path is easilydetermined, being the sum of the shortest measured distance from eachsensor 408 and 410 to the object 420, subtracted from the known totaldistance across conveyor 402 between the two sensors. One otherdimension, B, is easily determinable from the constant conveyor speedand elapsed time between the instant when corner 426 passes sensor 410and the end of the dark period when the LED beam again strikes receiver406. The "X" and "Y" distances give an apparent "footprint" for object420 which is, in actuality, larger than object 420 when the sides ofobject 420 are not parallel to conveyor path 412. In order to obtain theactual dimensions "L" and "W" of an object 420, X, Y, and B are employedas follows:

As shown in FIG. 9 of the drawings, the "footprint" of object 420 ismuch larger than its actual dimensions L and W. To determine L and W:

    Y.sub.1 +B=Y

    X.sub.1 +Z=X

this relationship equates to:

    L cos A+W sin A=Y

    L sin A+W cos A=X

which may also be represented as:

    LZ/W+B=Y                                                   (1)

    LB/W+Z=X                                                   (2)

Dividing Equation (2) by B yields: ##EQU1## Substituting (3) into (1) weobtain: ##EQU2## Multiplying by B, this yields:

    (X-Z)Z+B.sup.2 =YB;

or

    -Z.sup.2 XZ+B.sup.2 -YB=0;

or

    Z.sup.2 +(-X)Z+(BY-B.sup.2)=0

Therefore, ##EQU3## and given Z and W, L=W(X-Z)/B. From equation (4), itis evident that Z may have two values, and thus there may be twodistinct pairs of L and W, the second pair defining object 420 in brokenlines on FIG. 9. But, returning again to equation (4), the values of Zare symmetric about X/2. Returning to FIG. 9, it is evident that sensor426 measures one "Z" value at the leading edge and one at the trailingedge of object 420. Therefore, if the leading edge shows a value ofZ>X/2 and the trailing edge shows a value of Z<X/2, then Z<X/2, and thesmaller value of Z is employed to obtain L and W of object 420. If theleading edge Z<X/2 and the trailing edge Z>X/2, the larger value of Z isemployed to obtain L and W of object 420. If the values for Z are thesame at the leading and trailing edges, then there is only one solutionfor L and W.

Of course, in the unlikely event that object 420 is, in fact, perfectlyaligned with conveyor path 412, the readings from sensors 408 and 410will remain constant throughout the timed dark period, and the systemwill default to the trivial case wherein the timed distance Y is thelength of the object, and the measured distance X is the object width.

While system 400 has been described in use with a conveyor system 402,it should be understood that system 400 is not so limited. Any linearlymoving carrying or conveying means moving at a constant speed, such asan AGV, may be employed.

In some instances wherein it is desired to measure objects on the flydown a conveyor, photocells may be employed both to ensure that theweight measurement is accurate and to provide security against pilferageor miscoding of packages. In such an embodiment, system 500 as shown inFIG. 10, photocells 502, 504, 506, 508, 510 and 512 are linked to aprocess control unit 514 in a manner well known in the art and areplaced adjacent to a series of system components including skew conveyor520, scale 522, cubing system 524 and takeaway station 526. Photocells502-512 are preferably of the above-described through-beam type for thereasons previously discussed herein. Lead photocell 502 signals theprocess control unit 514 when a first package 530 or other object haspassed off of skew conveyor 520. The beam of photocell 504 is broken bythe passage of the first package 530 onto scale 522 and signals controlunit 514 to activate scale 522 when its beam is again unbroken after thetrailing edge of the first package has passed to ensure that the entirepackage is on the scale 522, and the correct package weight taken.Photocell 506 deactivates scale 522 via control unit 514 as the leadingend of the first package 530 breaks its beam before passing off of thescale 522 onto cubing system 524, again to ensure a correct weight. Ifthe first package 530 is longer than the scale 522, the process controlunit 514 will tag the weight reading as an error. Photocell 508 signalswhen the first package enters cubing system 524, initiating the entry ofa second package 532 from skew conveyor 520 onto scale 522. Photocell510 activates the width and height measuring ultrasonic sensors (notshown) of cubing system 524 when the leading edge of a package breaksits beam and commences a time out or dark period which is directlyrelated to the length of the object by the constant conveyor speed.Thus, weight, length, width and height of the package are ascertained ina manner previously described with respect to other embodiments andunder photocell control. Photocell 512 at takeaway station 526 signalswhen a package has left the entire weighing and measuring system 500after the bar code or other indicia on it has been read by an operatorat takeaway station 526 so as to match up the measured dimensions andweight with the appropriate package in the data gathering portion of thecontrol unit 514.

In furtherance of error and pilferage prevention, timed "windows" arebuilt into the operation sequence of system 500. For example, given theknown speed of the conveyor system, a package is normally on scale 522for a maximum, fixed period of time. If a package passes photocell 502but does not break the beam of 508 in a given time, the system signalsthat the package is missing. Likewise, if the package passes into cubingsystem 524 and triggers photocell 508 but does not trigger photocell 510within a given period of time, the system notes that the package ismissing. Further, the operator at takeaway station 526 has a certainamount of time to perform his or her function after the package passesphotocell 510. If the package does not pass photocell 512 during theaforementioned takeaway station window, the skew conveyor 520 stops sothat the operator is not inundated with packages, and again an errorsignal is generated to note a potential problem. At any given instant,there are only two packages in the queue in system 500. If any errorsignals occur, the second, trailing package in the system (the first,leading one presumably being missing for some reason) will continue totakeaway station 526, but no new packages will be fed from skew conveyor520. The aforementioned time windows are set in view of the speed of theconveyor system and the normal time required for operations beingperformed at takeaway station 526. Thus, pilferage is virtuallyeliminated from the time a package enters system 500 until its exittherefrom. Further, packages falling off of a conveyor or being removedduring the measuring process, which could result in a package beingerroneously associated with the weight and/or dimensions of a priorpackage in queue, are eliminated.

Calibration of the ultrasound sensors of the present invention may alsobe more readily and repeatedly effected via the use of a battery-backedRAM autocalibration system. Operation of the calibration system is shownin flow chart form in FIG. 11, and is as follows. An "Install" commandis given to the system which prompts the user to remove all objects fromthe sensor field. Each of the sensors is then fired individually, andthe number of time counts from each sensor to and from an empty platformis recorded. The system then prompts the user to insert a target of 12"extent (by way of example and not limitation) in each dimensionorientation being calibrated on the measuring platform, the sensors arefired again, and the counts per inch (CPI) for each individual sensorare determined by subtracting the total counts resulting from the 12"target firing from those resulting from the empty platform firing, anddividing by 12. The distance from the back wall of the empty platform tothe sensor is then calculated by dividing the "zero" or empty platform,count by the CPI. This base or "zero" distance is used in measuringobjects by firing the sensor at the object, calculating the distancebetween the sensor and the object, then subtracting it from the zerodistance to get the object dimension. While the CPI can vary withenvironmental conditions, as previously noted, the distance between thesensor face and the platform wall remains constant, so periodic sensorfirings onto the empty platform subsequent to the initial calibrationresult in automatic adjustment of the CPI figure to the fixed, knowndistance.

FIGS. 12 and 13 of the drawings depict a preferred embodiment 600 ofapparatus for effecting measurements used in the measurement methoddescribed with respect to system 400 and FIG. 9. System 600 is employedin conjunction with a linearly moving conveyor system 602, and includesan infrared (IR) light curtain system 604 disposed perpendicular to theconveyor path, and an ultrasonic sensor system 606 having at least oneultrasonic transducer or sensor of the type previously described above.The light curtain system 604 includes an IR emitter 608 and an IRreceiver 610, one disposed horizontally above and perpendicular toconveyor 602, and the other in alignment therewith and disposedhorizontally with its top surface at the level of, perpendicular to, andbetween feed conveyor 612 and takeoff conveyor 614 of conveyor system602. While IR emitter 608 is shown in FIG. 13 to be above conveyorsystem 602 and IR receiver 610 is shown to be therebelow, the emitterand receiver unit positions may be interchanged, as long as the emitterand receiver are disposed so that each light emitting element in the IRemitter 608 is aligned with its companion receiving element in IRreceiver 610.

A suitable light curtain system for use in the present invention is theaforementioned BEAM-ARRAY system offered by Banner EngineeringCorporation of Minneapolis, Minn. In the preferred embodiment, by way ofexample and not by limitation, a four (4) foot length Model BME448Aemitter is employed in alignment with a four (4) foot BMR448A receiver.IR emitter 608 employs infrared light emitting diodes (LED's) on 0.25inch centers, and IR receiver 610 employs a like number ofphototransistors centered on the same intervals. The LED's are firedsequentially along the length of the emitter 608. Each emitted LED beamis directed to its correspondingly aligned phototransistor in receiver610.

Ultrasonic sensor system 606 includes at least one downwardly facingultrasonic emitter/receiver transducer 616, but the preferred embodimentemploys four (4) such transducers or sensors 616, aligned in a row aboveand perpendicular to the path of conveyor system 602. While notessential to the operation of system 600, it is preferred forcompactness that sensors 616 be mounted on the same frame 618 as IRlight curtain emitter 608. Sensors 616 are disposed at a common distanceabove the surface of conveyor system 602, and are multiplexed. Whenfired, all of the sensors 616 simultaneously emit ultrasonic waveshaving substantially identical velocities, and the first returningsignal reflected from an object 620 on the conveyor system indicates theclosest, or in this instance, the highest part of the object and thusits maximum height. The first returning signal is accepted by a controlunit associated with system 600, converted to a distance in the mannerpreviously described, and subtracted from the known height of the sensorface above the conveyor surface. The remaining signals are gated out andthus disregarded. While sensors 612 have been depicted in a linear arrayoriented perpendicularly to the conveyor system 602, this is notrequired and any grouping which covers the entire width of the conveyorsystem may be employed.

In order to ascertain the true length and width of a rectangular object620 according to the methodology previously described with respect tosystem 400 and FIG. 9 of the drawings, conveyor system 602 must moveobject 620 at a substantially constant linear rate past light curtainsystem 604. The rate of speed is not important, as long as it does notexceed the speed at which the light curtain 604 can sequence through allof the emitter-receiver combinations of LED's and phototransistors. Forexample, when the aforementioned BEAM-ARRAY light curtain is employed inthe present invention, with LED/phototransistor pairs at 0.25 inchintervals and a factory preset scan rate of 4 milliseconds per foot ofarray length, or 16 milliseconds to complete a scan using a four footlight curtain. If an object 620 is passing traversing through thecurtain at 300 feet per minute velocity, it will travel 0.96 inchesduring a single scan of the light curtain, or an approximate accuracy ofwithin one (1) inch. Of course, if the scan rate were to be increased byemploying a higher clock speed with a clock external to the system (oremploying a higher speed internal clock), and/or the conveyor speed wasreduced, accuracy could be increased. For example, using a scan rate of2 milliseconds per foot and a conveyor speed to 150 feet per minute, anobject 620 will travel only 0.24 inches per scanning cycle. Since thelight curtain sensors are at 0.25 inch intervals, the system 600 wouldthen be operating at its maximum possible accuracy.

It is desirable to operate light curtain 604 in a continuous scan mode,with each scanning cycle immediately following completion of thepreceding one. The scanning cycles can be activated continuously whilethe conveyor is in motion, or may be triggered by a beam-interrupt typephotocell, as previously described. In the preferred embodiment shown inFIGS. 12 and 13, a separate photocell trigger 622 is employed.

Operation of system 600 is as follows. When an object 620 approachessystem 600 on conveyor 602, it breaks the beam of photocell trigger 622,activating the light curtain system 604 in a continuous scan mode. Aseach scan is conducted, phototransistors covered by the object 620 willbe blocked from receiving a light beam from their associated LED,indicating the width of that section of object 620 perpendicular to thepath of the conveyor system 602. Thus, the width and time of passage ofeach succeeding section of object 620 is measured as it passes throughlight curtain 604, as well as the position of the section on theconveyor.

The presence and the time of passage of leading edge 630 of object 620is sensed by the light curtain when an emitter/receiver pair is firstobstructed, and the time of passage of trailing edge 632 is similarlysensed when all phototransistors of IR receiver 610 become uncovered. Itshould be noted that the presence and time of passage of the object 620may also be determined by using the dark period of the beam-interrupttype photocell trigger 622. Using the time of object passage, it isthereby possible to ascertain the apparent length Y of object 620. Thismay be effected in several ways. One way is to set conveyor system 602to a selected speed, which is then multiplied by the time of objectpassage. Another, more preferred methodology uses no preset speed, butonly a control object of a known length, for example, one foot, which isplaced on conveyor system 602 to pass through light curtain 604. Thetime of passage is then recorded by system 600 against the controlobject length, converted to a distance per time multiplier, and employedby a system 600 to measurement of unknown objects. Finally, aspeedometer might be used to monitor conveyor speed, but thisalternative is also less preferred.

The apparent width X of object 620 is obtained during the continuousscan process of the light curtain, as the system 600 records allconsecutive scans of object 620, stores in buffer memory, then sorts tolocate the position of the farthest laterally outwardly extendingcorners 634 and 636 on object 620, and computes the distancetherebetween, taken in a direction perpendicular to the conveyor path.

Finally, one other dimension, B, is easily determinable since the timeof passage of corner 636 through light curtain 604 has been recorded, aswell as the time of passage of trailing edge 632. Subtracting to obtainelapsed time and multiplying by the aforementioned distance per timemultiplier, distance B is calculated.

Given X, Y and B, the actual length L and actual width W may then becalculated in the manner previously described with respect to FIG. 9.

Ultrasonic sensor system 606 is likewise triggered by photocell trigger622, and the array of multiplexed sensors 612 fired at several presetintervals as previously described to obtain the maximum height of theobject 620. While a single firing is adequate for objects of constantheight, such as cubic boxes, if the object is a load of various items ona pallet this will not be the case, and multiple firings are necessary.

Once the true length and width of object 620 are ascertained, and themaximum height, the cubic volume or spatial volume of the object may becomputed for use as previously described.

It is possible to utilize a light curtain height sensor in lieu of anultrasonic system, but this alternative is not preferred in view of thehigh cost of light curtain systems.

It is thus apparent that a novel and unobvious measuring method andapparatus has been described in a variety of embodiments. Manyadditions, deletions, and modifications to the preferred embodiments maybe made without departing from the scope of the invention as hereinafterclaimed.

What is claimed is:
 1. A method of determining the actual dimensions ofa linearly moving object of substantially rectangular cross-section inthe horizontal plane, the sides of which object are in non-parallelrelationship to the direction of travel, comprising:linearly moving saidobject at a constant speed; determining the apparent length of saidobject by measuring the travel time thereof past a first point on theline of object travel and multiplying said travel object travel time bysaid constant speed; determining the apparent width of said object bysensing the positions of the outermost corners of the object, taken in adirection perpendicular to said direction of object travel, andcomputing the distance between said outermost corners in saidperpendicular direction; determining a distance taken in the path ofobject travel between one of said outermost corners and the trailingedge of said object by measuring the travel time between the passage ofsaid outermost corner and that of said trailing edge past a secondcommon point on the line of object travel and multiplying said corner totrailing edge travel time by said constant speed; and calculating theactual length and width of said object utilizing said determinedapparent length, apparent width, and outermost object corner to trailingedge distance.
 2. The method of claim 1 wherein said point is determinedby a photocell beam.
 3. The method of claim 1 wherein said step ofsensing is performed using a light curtain oriented perpendicularly tosaid direction of object travel.
 4. The method of claim 1, furtherincluding the step of sensing the maximum height of said object.
 5. Themethod of claim 4, further including computing the spatial volume ofsaid object by multiplying said actual length, actual width and maximumheight.
 6. The method of claim 4, wherein said step of sensing saidmaximum height is effected ultrasonically.
 7. The method of claim 1,wherein said first point and said second point are the same.
 8. Anapparatus for determining the actual dimensions of a linearly movingobject of substantially rectangular cross-section in the horizontalplane, the sides of which object are in non-parallel relationship to thedirection of object travel, comprising:conveying means for moving saidobject at a constant speed on a linear path past a point; meansassociated with said conveying means for measuring the apparent lengthof said object in a direction parallel to said linear path, the apparentwidth of said object in a direction perpendicular to said linear path,and the distance in a direction parallel to said linear path between acorner of said object defining one extent of said apparent width and thetrailing edge of said object; and computing means for calculating theactual length and width of said object from said apparent length,apparent width and said corner to trailing edge distance.
 9. Theapparatus of claim 8, wherein said measuring means includes means forsensing the arrival of a leading edge and of a trailing edge of saidobject at said point and for ascertaining the time between saidarrivals, and said computing means includes means for multiplying saidtime by a constant based upon said constant conveying means speed toascertain said apparent length.
 10. The apparatus of claim 9, whereinsaid measuring means includes means for providing said constant basedupon the travel time of a control object of known length past saidpoint.
 11. The apparatus of claim 9, wherein said measuring meansincludes light curtain means dispersed transversely across said linearpath for measuring said apparent width.
 12. The apparatus of claim 11,wherein said measuring means further includes means for repeatedlyactivating said light curtain means to scan across said linear path, forreceiving data from said repeated scans of said light curtain, forstoring said scan data, for relating data from each of said scans to aspecific instant in time, for sorting said scan data to ascertain thearrival time at said light curtain associated with at least one of twoobject corners defining said one extent of said apparent width, forsensing the arrival time of a trailing edge of said object at said lightcurtain, for subtracting said apparent width one extent arrival timefrom said trailing edge arrival time, and said computing means includesmeans for multiplying the arrival time difference by a constant basedupon said constant conveying means speed to ascertain said corner totrailing edge distance.
 13. The apparatus of claim 8, wherein saidmeasuring means includes light curtain means dispersed transverselyacross said linear path for measuring said apparent width.
 14. Theapparatus of claim 13, wherein said measuring means further includesmeans for repeatedly activating said light curtain means to scan acrosssaid linear path, for receiving data from said repeated scans of saidlight curtain, for storing said scan data, for relating data from eachof said scans to a specific instant in time, for sorting said scan datato ascertain the arrival time associated with at least one of two pointson said object defining said one extent of said apparent width, forsensing the arrival time of a trailing edge of said object past saidpoint, for subtracting said apparent width one extent arrival time fromsaid trailing edge arrival time, and said computing means includes meansfor multiplying the arrival time difference by a constant based uponsaid constant conveying means speed to ascertain said corner to trailingedge distance.
 15. The apparatus of claim 8, further including means formeasuring the maximum height of said object.
 16. The apparatus of claim15, wherein said height measuring means is ultrasonic.
 17. The apparatusof claim 16, wherein said ultrasonic means comprises an array includinga plurality of ultrasonic sensors.
 18. The apparatus of claim 17,wherein said ultrasonic sensor array comprises a linear array ofdownwardly-facing ultrasonic sensors disposed over and transverse to thepath of said conveying means.
 19. The apparatus of claim 15, whereinsaid computing means includes means for computing the spatial volume ofsaid object from said length, width and maximum height.